A M-bridge class-D audio amplifier for portable applications and a method of driving a three-wire audio output device comprises a stereo signal source producing a first and second input stereo digital signal; circuitry adapted to receive the first and second input stereo digital signals and produce three stereo signals comprising a first, second, and third digital signal, wherein the three stereo signals generate pulse-width modulation (PWM) waves comprising a first, second, and third digital signal PWM wave; exactly three pairs of MOSFETs driven by the first, second, and third digital signal PWM waves; and a three-wire speaker system comprising a first wire driven by the first digital signal PWM wave; a second wire driven by the second digital signal PWM wave; and a common wire driven by the third digital signal PWM wave.